Effective fracture placement using alternate fracturing

ABSTRACT

Alternate (Out-Of-Sequence) Pinpoint Fracturing has been tested in Western Siberia and Western Canada. It aims to create fracture complexity via reducing the stress anisotropy to improve fracture network connectivity. It is initiated by fracturing Stages 1 and then 3 (Outside Fracs) followed by Stage 2 (Centre Frac). A fracture model is calibrated using Alternate Pinpoint Fracturing trials in Western Canada. The calibrated fracture model is used to evaluate Alternate Pinpoint Fracturing under various geomechanical and treatment conditions for identifying strategies in maximising its benefits. This integrated geomechanical study reveals that: (1) Centre Fracs tend to have a larger surface area and smaller conductivity versus Outside Fracs, (2) Centre Fracs tend to be narrower and shorter (versus Outside Fracs) if sufficient out-of-zone growth is attained in the absence of strong fracture height containment, making it an option for penetrating multi-stacked zones in one treatment, and (3) Where Centre Fracs are shorter or near-well fracture complexity is generated, it can be considered in treating the child wells to reduce frac hits.

KEYWORDS:

• Stress anisotropy
• Shuttle Frac
• Induced stress shadowing
• Fracture complexity
• Planes of weakness
• Stress-relief fractures

Nomenclature

Symbols	=
a	=	Fracture half-height [m]
Af	=	Fracture effective flowing surface area [m2]
Cdp	=	Pressure-dependent leak-off coefficient [1/kPa]
Co	=	Constant matrix leak-off coefficient [1/kPa]
Cp	=	Leak-off coefficient [1/kPa]
Dtv	=	True vertical depth [m]
E	=	Young’s modulus [GPa]
hf	=	Fracture height [m]
i	=	Injection rate [m3/min]
kres	=	Reservoir matrix permeability [md]
kfwf	=	Fracture intrinsic conductivity [md.m]
Le	=	Well length [m]
P	=	Pressure in the hydraulic fracture [MPa]
Pc	=	Closure pressure [MPa]
Pn	=	Net fracturing pressure [MPa]
Po	=	Overburden pressure [MPa]
Poff	=	Pore pressure offset [MPa]
Pp	=	Pore pressure [MPa]
PR	=	Poisson’s ratio [-]
re	=	Sum of the inner and outer reservoir lengths [m]
t	=	Variable transverse exponent [-]
wf	=	Fracture width [mm]
xi	=	Stimulated reservoir volume half-width [m]
Xc	=	Created fracture half-length [m]
Xf	=	Effective flowing half-length [m]
Yi	=	Inner reservoir half-length [m]
Z	=	Distance from the fracture face [m]
Greek Letters	=
αh	=	Horizontal Biot’s poroelastic constant [-]
αv	=	Biot’s poroelastic coefficient in the vertical plane [-]
ΔP	=	Fluid pressure above the CFOP [kPa]
∆σ	=	Horizontal stress anisotropy [MPa]
εx	=	Regional horizontal strain [microstrains]
γo	=	Overburden gradient [kPa/m]
γp	=	Pore pressure gradient [kPa/m]
µ	=	Viscosity [cp, mPa.s]
v	=	Poisson’s ratio [-]
ρb	=	Grain bulk density [g/cm3]
σ	=	Residual stress [MPa]
σc	=	Closure stress [MPa]
σext	=	Externally generated stress [MPa]
σh,min	=	Minimum horizontal in-situ net effective stress [MPa]
σh,max	=	Maximum horizontal in-situ net effective stress [MPa]
σtect	=	Regional horizontal tectonic stress [MPa]
Acronyms	=
BHA	=	Bottom hole assembly
BRF	=	Brittleness factor
CFOP	=	Critical fissure opening pressure [MPa]
DFIT	=	Diagnostic fracture injection test
DTC	=	Compressional travel time [µs/m]
ISIP	=	Instantaneous shut-in pressure [MPa]
MD	=	Measured depth [m]
MSF	=	Modulus stiffness factor [1/kPa]
PDL	=	Pressure-dependent leak-off
PR	=	Poisson’s ratio [-]
PZS	=	Process zone stress [MPa]
SFC	=	Shift-Frac-Close
SRV	=	Stimulated reservoir volume
SW	=	Slickwater
TVD	=	True vertical depth [m]
WCSB	=	Western Canadian sedimentary basin
XL	=	Cross-linked
YM	=	Young’s modulus [GPa]

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.